232 



ELECTRO-PHYSIOLOGY 



CHAP. 



however, in the optic nerve of the fish (Ktihne, 9), where the fibres 

 have no constrictions, and also in non-mednllated nerve (Bieder- 

 inann, 3), although in a less marked degree, so that there is no 

 adequate reason for assuming definite anatomical boundaries within 

 the continuity of the axis -cylinder, at which the process of 

 mortification shall be arrested. If the fact that the separate 

 cell-individuals in cardiac and smooth muscle are directly united 

 by plasma-bridges is of universal application, the consequences of 

 renewing the section can only indicate that the death-process is 

 arrested at some distance from the cut surface, without confining 

 it within preordained anatomical barriers. 



Nerve, like muscle, can be excited by its own demarcation current. 

 The facts relating to this subject have been familiar since the days 



FIG. 201. Excitation of nerve by its own current. 



of Galvani, and have more especially been investigated by Kiihne 

 and Hering (11). Galvani introduced the nerve of a rheoscopic 

 leg into an open circuit, and allowed the nerve of another leg, 

 completely isolated from the first, to fall upon the circuit, in such 

 a way that the cross-section of the first nerve formed one of the 

 two points of contact. Both legs twitch in a successful experi- 

 ment. Du Bois-Reymond laid the central end (transverse and 

 longitudinal sections) of a sciatic nerve, still connected with the leg, 

 across the pads of his zinc trough-electrodes, making and breaking 

 the nerve current by means of a mercury key. " The leg twitched 

 at closure and at opening, in some cases on breaking the circuit 

 only." Du Bois-Reymond subsequently simplified this experi- 

 ment by placing two long pads of filter-paper saturated witli salt 

 solution close together upon an insulating stage, and laying acr< iss 

 them the long and transverse sections of the rheoscopic nerve. 



